This invention relates to an electromotive chain saw.
In a conventional electromotive chain saw, a hand guard for protecting an operator""s hands is provided in front of a handle. Additionally, a brake band is wound around a brake drum for stopping the operation of a cutting chain. By operating the hand guard and pulling one end of the brake band, the brake drum is tightened with the brake band, thereby stopping the cutting chain.
However, in such electromotive chain saws, even after a trigger member is released and a motor drive switch is turned off, the inertial rotation of the motor often results in the rotation of the cutting chain for several seconds. If the rotating chain contacts or hits the ground, it is often damaged, thereby requiring the replacement of the chain itself. The material in process is also inadvertently damaged. Furthermore, the operator cannot go to the subsequent steps of work until the chain is completely stopped. Thus, the work efficiency is deteriorated.
To solve the aforementioned problem, it is proposed in Japanese examined and published patent application No. 657401 that a circuit having a brake winding is provided in an electromotive motor and the circuit is closed when a trigger member is released, for the purpose of dynamic braking without any impact.
Such gradual stopping of the chain achieved in the proposal fails to satisfy a recent demand for stopping the chain quickly, for example, within one second after the trigger member is released.
Wherefore, an object of the present invention is to provide a brake device for a chain saw that can quickly stop the rotation of a cutting chain when a trigger member is released.
To achieve this or other object, the present invention provides an electromotive chain saw, having an electric motor for providing a rotary drive force to a drive sprocket on which a cutting chain is wound, a trigger member for energizing the electric motor when turned on and for stopping the electric motor when turned off, a trigger link mechanical brake for being engaged with a brake drum secured to the drive sprocket when the trigger member is turned off and for being disengaged from the brake drum when the trigger member is turned on, and a trigger link brake circuit for cooperating with the trigger member and applying a dynamic braking force to the electric motor when the trigger member is turned off.
In operation of the electromotive chain saw, when the trigger member is turned off, both the trigger link mechanical brake and the trigger link brake circuit are operated. The mechanical braking of the brake drum and the electric braking of the electric motor are concurrently carried out. As a result, the cutting chain is stopped directly stopped by the trigger link mechanical brake and indirectly by the trigger link brake circuit, more quickly as compared with the provision of only the trigger link brake circuit or only the trigger link mechanical brake.
The number of rotations of the electric motor can be quickly decreased, in the electromotive chain saw in which the rotary drive force is transmitted from the electric motor via a centrifugal clutch mechanism to the drive sprocket. This occurs, when a predetermined number of rotations of the electric motor is reached or exceeded and no rotary drive force is transmitted to the drive sprocket when the number of rotations is lower than the predetermined number of rotations. Since the centrifugal clutch is quickly released, the load on the trigger link mechanical brake can be reduced. Therefore, the cutting chain can be instantly stopped and the trigger link mechanical brake results in increased durability.
Instead of the centrifugal clutch mechanism, the clutch mechanism can be composed of a plurality of engagement teeth formed on the brake drum, an engagement member rotated together with a rotation shaft rotated by the electric motor and slidable in an axial direction relative to the rotation shaft for engaging with the engagement teeth on the brake drum, and an urging member for pushing and urging the engagement member toward the brake drum. The electromotive chain saw is further provided with a clutch release member for releasing the engagement of the clutch mechanism by pushing back the engagement member against the urging member when the trigger member is moved from its ON position to its OFF position.
In the conventional electromotive chain saw having the clutch release member, the cutting chain can be instantly stopped with a mechanical brake force when the trigger member is turned off. This occurs while gradually stopping the inertial rotation of the electric motor. In the present invention, the cutting chain and the electric motor are concurrently stopped, thereby eliminating discomfort given to an operator when the electric motor is inertially rotated even after the cutting chain is stopped.
In addition, a further advantage of the present invention is provided by the provision of the aforementioned dynamic braking. In actual operation of the conventional electromotive chain saw, when the released trigger member is turned on immediately after turning off, if the motor is still inertial rotated, the rotating clutch components are going to be engaged with one another and the rotary drive force of the electric motor is applied to an engagement detent and other components, thereby impairing the durability of the clutch mechanism. However, in the present invention, the electric motor is also stopped by the dynamic braking. Therefore, the durability of the engagement detent and other clutch components is enhanced.
In the electromotive chain saw, a conventional brake band can be wound around the brake drum, and a trigger link mechanical brake can be provided. By operating a hand guard and pulling the connected end of the brake band, the brake drum is tightened with the brake band, thereby stopping the cutting chain against the rotary drive force of the electric motor. Also, by releasing the trigger member, the cutting chain is stopped directly by the trigger link mechanical brake and indirectly by the trigger link brake circuit.
The trigger link mechanical brake of the electromotive chain saw is provided with an operable member secured to an end of the brake band, for cooperating with the trigger member, such that the brake band is pulled and tightened when the trigger member is released and the brake band is released or loosened when the trigger member is turned on.
An operable member is provided which is secured to one end of the brake band having the other end operatively connected to the hand guard, for cooperating with the trigger member. This adds only a slight structural change to the conventional structure and requires no complicated mechanical arrangement. When the trigger member is released, the end of the brake band, opposite the end operatively connected with the hand guard, is pulled, thereby tightening the brake band for stopping the cutting chain. Therefore, when braking by the trigger link mechanical brake is employed a frictional force is applied to the opposed part of the brake band resulting in a frictional force at the time of braking by the operation of the hand guard.
The trigger link mechanical brake can be provided with a brake shoe for engaging with the outer periphery of the brake drum, an urging member for normally urging or pressing the brake shoe to the brake drum, and a pulling member for disconnecting the brake shoe from the brake drum against the urging member when the trigger member is depressed or turned on.
The brake shoe is provided separately from the brake band and is operatively connected to the hand guard. When the trigger member is released, the brake shoe applies a braking force without giving any frictional force to the brake band.
Alternatively, the trigger link mechanical brake can be provided with a brake shoe operatively connected to the trigger member for engaging with the inner periphery of the brake drum. When the trigger member is released, the brake shoe is pushed onto the brake drum, and when the trigger member is turned on, the brake shoe is disconnected from the brake drum.
The trigger link brake circuit of the electromotive chain saw is provided with a main winding and a brake winding both in a field slot. The supply of a drive current to an armature and the main winding and the supply of a counter electromotive force arising with the brake winding to the armature are changed over with a single-pole double-throw switch, thereby driving and braking the electric motor. When the single-pole double-throw switch is changed over such that the drive current is supplied to the armature and the main winding, one end of the brake winding is disconnected from the armature via the single-pole double-throw switch, and the other end of the brake winding is disconnected from the main winding via a single pole switch.
During the operation of the electromotive chain saw, in the trigger link brake circuit, the brake winding is disconnected from the main winding by the single pole switch, and the brake winding is disconnected from the armature by the single-pole double-throw switch. Therefore, even when the main winding and the brake winding are wound in the same field slot, the brake winding and the main winding are completely insulated via the single pole switch and thus will not deteriorate and no field layer shortage thus occurs. Therefore, to provide the sufficient capabilities of the brake winding, the number of windings can be increased. The trigger link brake circuit is highly durable while it also fulfills its braking performance. For this purpose, the inexpensive single pole switch is provided, eliminating the need for a two-pole double-throw switch, which is cost effective.
To operate the electromotive chain saw, in the trigger link brake circuit, the single pole switch is switched over such that the brake winding is disconnected from the armature and the main winding. The clutch mechanism is engaged. Subsequently, the single-pole double-throw switch is changed over such that the power source is connected with the armature and the main winding.
To apply a braking force to the electromotive chain saw, the single-pole double-throw switch is changed over such that the power source is disconnected from the armature an the main winding and the brake winding is connected with the armature. The clutch mechanism is disconnected. Subsequently, the single pole switch is changed over such that the brake winding is connected with the armature.
When the electric motor is in operation and the single-pole double-throw switch is turned on, in the switching approach, no connection is made between the brake winding and the main winding, therefore, no field layer shortage arises.
Furthermore, when the chain saw is in operation, after the clutch mechanism is engaged, the single-pole double-throw switch is changed over to connect the power source with the main winding and the armature, and the electric motor is driven. When the chain saw is braked, after the single-pole double-throw switch is changed over to disconnect the power source from the main winding and the armature, the clutch mechanism is disengaged. The engagement and disengagement of the clutch mechanism can thus be easily carried out and the durability of the engagement detent can be enhanced.